A variety of automated or semi-automated chemical analyzers are known which utilize cuvettes for the chemical testing of samples placed therein. Generally, a predetermined amount of liquid sample, such as a biological fluid, is placed in the cuvette which is then transported through the instrument. As the cuvette is being transported, the instrument dispenses a quantity of reagent into the sample and monitors the resulting chemical reaction. Such monitoring is generally accomplished through use of an optical means which views the fluid sample through optically transparent portions of the cuvette.
In order to simplify the loading of the cuvettes into the instrument and facilitate their handling by the instrument once so loaded, proposals have been made to provide the cuvettes in the form a continuous integral strip. The individual cuvettes of the strip are designed to be relatively rigid, but the strip itself is provided with sufficient flexibility to ease its transport through the instrument. Furthermore, by making the cuvettes in a continuous strip form, they can be manufactured relatively inexpensively from suitable plastic material, thereby permitting their disposal after use. This is an important feature since it avoids the requirement for washing the cuvettes after use and avoids any possibility of cross contamination of fluid samples which could cause erroneous test results. A proposed cuvette system designed to meet these requirement is disclosed in U.S. Pat. No. 4,263,256.
In commonly owned copending U.S. patent application Ser. No. 559,016 and entitled "Cuvette Ssytem For Automated Chemical Analyzer", which is a continuation of U.S. patent application Ser. No. 284,842 filed July 20, 1981, both now abandoned, the disclosure of which applications are hereby incorporated by reference in their entirety herein, there is described a cuvette belt which comprises a matching pair of elongated, formed plastic strips which are joined together along corresponding faces thereof to form an integral belt. A series of regularly spaced chamber halves are formed transversely in each of the corresponding strip faces which define open-topped cuvette receptacles when the belt halves are joined.
As described, the cuvette belt is made by forming strip plastic material with a series of regularly spaced transverse (laterally extending) formed pockets so as to define two integral side-by-side belt halves. The formed strip is then divided longitudinally to separate the belt halves and the belt halves brought into register and joined together to form a completed cuvette belt.
Using such manufacturing techniques, cuvettes may be obtained with superior operating characteristics and dimensional accuracy previously obtainable only through use of injection molding techniques. This is important when optically analyzing samples in the cuvettes for which a precisely defined optical path through the cuvettes is required.
It is pointed out that it is possible by utilizing cold forming techniques to avoid optical degradation of the material due to heat. Further, an optical portion of the material may be restrained by clamping or other forming techniques during the pocket forming operation to avoid stretching or other deformation of portions of the pocket which form the sides of the cuvette. In this manner essentially all stretching of the material during the forming is limited to the side walls of the pockets and optical portions thereof are maintained stress-free and with a uniform thickness. Further, as described in the aforesaid application, the opposite side walls of each cuvette chamber, which form the optical portions, are made parallel thereby providing an optical path of precise length through the cuvette.
Reference is also made to commonly owned copending U.S. patent application Ser. No. 746,231, filed June 18, 1985, entitled "Cuvette Belt Manufacture and Process", the disclosure of which application is hereby incorporated by reference in its entirety herein. In that application is disclosed an alternative method for making cuvette belts of the kind comprising a matching pair of plastic strips, each of which is formed with chamber halves and which are joined together to form an integral cuvette belt with the chamber halves aligned to form the cuvette.
According to that method, the two strips of plastic material are identically formed with a series of regularly spaced formed pockets so as to define two integral side-by-side belt halves. The two formed strips are brought into register and joined together to form a composite strip defining two integral mirror image cuvette belts joined by their cuvette mouth ends. The composite strip is then divided longitudinally to separate the cuvette belts.
The present invention is concerned with improved techniques for the manufacture of such cuvette belts with the particular aim of controlling the optical characteristics of the cuvettes. Accordingly it is an object of the invention to provide a cuvette belt in which the optical path through the cuvettes is precisely defined and repeatable from one cuvette to the next when utilizing the belt in a chemical analyzer.